1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program and, in particular, to an image processing apparatus, an image processing method, and program which reduce noise components with high precision, by a determination processing whether or not noise exists and a noise reduction processing for each pixel.
2. Description of the Related Art
Noise components contained in a digital signal that is obtained from an image pickup element, an analog circuit in association with the image pickup element and an analog-to-digital (hereinafter referred to as A/D) converter are roughly categorized into random noise and spike noise. The random noise is generated in the image pickup element and the analog circuit, and has characteristics similar to those of white nose. The spike noise is mainly caused by an image pickup element such as a defective pixel therewithin.
Japanese Unexamined Patent Application Publication No. 2001-157057 discloses a random noise treating technique in which an amount of luminance noise is expressed in function relating to a signal level, the amount of luminance noise relating to the signal level is then estimated from the function, and frequency characteristics of filtering are then controlled based on the amount of luminance noise. In this way, a noise reduction process of random noise is performed with respect to the signal level.
As disclosed in Japanese Unexamined Patent Application Publication No. 2001-157057, the amount of random noise is represented by function N=abcD where N represents an amount of random noise and D represents a density value converted signal level. Here, a, b, and c represent constants, respectively, and are static values.
Japanese Unexamined Patent Application Publication No. 5-41867 discloses a spike noise treating technique in which the spike noise is detected by comparing each pixel with a maximum value or minimum value of each of surrounding pixels, and the pixel is replaced with the maximum value or the minimum value if determined as being spike noise. In this way, the noise reduction process is performed on the spike noise.